The present invention relates to a camera, or imaging apparatus, on board a satellite or similar spacecraft and having an imaging device and condensing means. More particularly, the present invention is concerned with a disturbance compensation system capable of correcting, on board, the optical axis displacements due to the attitude changes of the spacecraft on the orbit, vibrations due to movable parts included in the camera, and other disturbances, the focus displacements of the condensing means due to temperature changes, the fine position displacements of the imaging device due to positioning errors particular to a production line and vibrations ascribable to launching, etc.
Generally, an on-board camera for a satellite or similar spacecraft and having an imaging device and condensing means suffers from positioning errors particular to a production line, fine position displacements of the imaging device due to launching, misregistration of images due to vibrations ascribable to changes in attitude on the orbit and the operations of movable parts, relative misregistration of images between bands in the case of multiband optics (interband registration). To correct such displacements and misregistrations, it is a common practice to send data from the spacecraft to the ground stations and process images by software at the base station or, in the case of on-board correction, to change the angular position of a mirror located in front of the condensing means. However, the software scheme needs the development of special programs and requires manual operations for image processing, resulting in time- and labor-consuming work. As a result, real-time correction is not available with this kind of scheme. Furthermore, such image processing cannot correct the displacements of the focal position. Although the mirror scheme is capable of correcting the orientation of the optical axis by real-time processing, it cannot correct, in the case of multiband optics, the misregistration between bands. Another problem with the mirror scheme is that the diameter of the mirror depends on an aperture diameter of an optical condensing means. Therefore, the more the optical condensing means is large, the more an appearance and mass of the mirror and a mirror drive mechanism. As a result of the problem, it is difficult for the mirror scheme to be applicated as the system to spacecraft on board equipment which should be light weight and consume a minimum of power. In addition, rapid response is not achievable due to the heavy mirror.